a. Field of the Invention
The invention relates to photoconductive film forming nitropyrene-formaldehyde resins, processes for producing such resins, and photoconductive films prepared from such resins.
B. Description of the Prior Art
A variety of organic photoconductors are known. Of these, poly-N-vinyl carbazole is the most widely employed, although others such as N-alkyl derivatives of poly-N-vinyl carbazole, anthracene, perylene, and various derivatives of acylhydrazones, oxadiazoles, triazoles, pyrazolines, imidazolones, benzimidazoles, benzoxazoles and benzothiazoles have also been described. Some organic photoconductors are readily deposited from a solvent in the form of a film. Others are not so readily deposited. Among those organic photoconductors which do not have satisfactory film forming properties, there are included bromopyrene-formaldehyde resins such as disclosed in Aktuelle Probleme Der Electrophotographie, 3 Europaishes Kolloquium, Aug., 1971. These resins, moreover, do not form a good adhesive bond on the support. As a result, it has not been possible to take full advantage of the photoconductivity of the resins. The addition of plasticizers to improve the film forming characteristics of the base resin, or the admixture of the base resin with other more adhesive resins to improve the adhesive quality of the base resin, has not produced satisfactory results. In both cases, the additives adversely affect the photoconductivity of the base resin.
Organic photoconductors are generally superior to inorganic photoconductors because they are lighter, and because they manifest greater flexibility, light transmission and homogeneity. Because of these improved properties, unsupported films of photoconductive materials are useful as second originals in diazo copying systems, and in electrophotographic machines employing belt type photosensitive materials.